Highly functionalized, polar perfluorinated polyethers (“PFPE”) are currently used as lubricants in a variety of high-performance applications, for example to lubricate hard disc drive (“HDD”) media, as well as to lubricate precision mechanical instruments to minimize mechanical wear. PFPEs also function as anti-wetting and/or corrosion-protective agents on metal-containing substrates, particularly in magnetic recording devices such as magnetic recording disks and magnetic recording heads. See, for example, U.S. Patent Publication No. 2002/0090536 to Dai et al., which describes novel metal salts of perfluorinated polyethers.
One of the most widely used lubricants is Fomblin®Z-Tetraol, a tetra-hydroxyl functionalized PFPE (Solvay Solexis, Inc.). Unfortunately, PFPEs tend to have poor solubility in relatively non-polar fluorinated solvents, which are commonly used as the lube bath solvents for deposition of functionalized PFPEs on disks for HDD applications. Even at low concentrations, a Fomblin®Z-Tetraol solution in a hydrofluorocarbon or hydrofluoroether solvent, is found to be cloudy and turbid due to the poor solubility of the PFPE lubricant in the fluorinated solvents.
U.S. Pat. No. 5,663,127 to Flynn et al., describes the use of perfluorinated non-aromatic cyclic solvents as replacements for the non-polar fluorinated solvents, as one means of improving the dissolution properties of functionalized, polar PFPEs. However, such heterocyclic solvents can be costly.
To develop a lubricant that does not use conventional PFPEs, which are only soluble in fluorinated solvents, U.S. Pat. No. 6,093,495 to Falcone describes a water-soluble salt of a perfluoro polyether alcohol which is readily soluble in aqueous solvents.
Therefore, in spite of the advances in the art, there is a continuing need to develop improved methods of functionalized PFPE deposition for HDD applications. The present invention addresses those needs by improving the solubility of PFPEs in lube bath solvents using an alcohol or cyclic ether.